The invention relates to a process by which optimal shifting points of an electrohydraulically controlled automatic transmission can be determined.
It is a well known fact that, in automatic transmissions, the decision making of the driver is taken over by automatic controls. Initially, only one single value of upshifting or downshifting velocity was established for the individual gears. However, these controls were unable to consider either loading of the motor vehicle, or ascent or intention of overtaking. Accordingly, several solutions have been developed for making controls more sensitive.
As is apparent from one of the articles of the periodical, Avtomobiljana promuslennoszty 1986/2, with Soviet GMP automatic transmissions the loading range of the motor was divided in three sections. That means technically that the stroke length of the gas pedal is divided into three sections, and different points of gear change are defined for each section. Essentially a similar solution is described in the Patent U.S.-PS No. 4,468,987. In this case, too, conclusion is drawn from the position of the throttle pedal in respect to the load, while a series of points of gear change was defined for the unloaded, loaded and braking state. However, these solutions are not able to consider properly the intentions of the driver to accelerate the vehicle.
The solution according to the U.S.-PS No. 4,414,863 represents a more complete arrangement. With this system, in addition to the separation of loading sections, gear change is made softer by delayed shifting. A further advantage is that a program is provided for acceleration, which hinders down shifting after having already shifted up in course of acceleration. In this case "full extension" of the motor is achieved.
The solution according to the German DE-PS 1,580,011 considers loading in a quite different way. In this case electric signals formed from the position of the throttle pedal and velocity are added, and on the basis of the sum obtained the system selects the proper series of points of gear change.
With these systems it has been tried to approach ideal ways of driving so that more and more series of points of gear change were determined. The German Patent Specification DE-OS 2,756,719 gives an example for a solution which was developed for earthwork machines. Special series of points of gear change were determined for the operation on highways and in the performance of work.
Similar solutions are disclosed in the German Patent Specifications DE-PS 1,958,944 and DE-PS 2,424,607, as well as in the U.S.-PS No. 4,263,826. A most interesting feature of the last-mentioned is that complete control is realized hydraulically and the load is examined on basis of the number of revolutions of the motor.
The German Patent Specification DE-PS 1,954,783 gives a solution for further possibilities of correction. With this solution the driver may increase the automatically selected points of gear change by means of a change-over switch.
According to the solution as specified in the German Patent DE 2,013,079 the driver may influence control during the ascent. At the same time, the control itself considers certain changes in traffic conditions, such as the angle of the slope acceleration of the vehicle, and curvature of the road.
With the solution according to U.S.-PS No. 4,044,634 a detector measures the acceleration of the vehicle. In a case of intense acceleration, the control does not change up to a higher gear.
In addition to determining the points of gear change, another problem used to arise in connection with automatic transmissions. In the course of a gear change, the number of revolutions of the crankshaft of the motor will be different from the number of revolutions of the driving shaft of the transmission, so that inelastic operation and impulsive loads can occur. With one known solution, clutches are operated with delay, meanwhile the number of revolutions of the motor is readjusted. Readjustment used to be performed generally during a period of constant value. The specification of GB-PS 2,087,005 discloses a more sensitive control, at which the speed of closing and opening of the short-circuiting clutch is regulated as a function of the extent of throttling, of the velocity of the vehicle and of gear change.
The solution according to the German Patent Specification DE 2,537,006 represents a further trend of development, which is well suitable for both the short-circuiting and gear changing clutches. With this solution the pressure of the hydraulic liquid is controlled in accordance with the loaded state of the motor. Conclusions on the load are drawn from the position of the throttle pedal and the number of revolutions of the motor. Additionally, the driver may influence the situation by means of a switch.
From the survey of the different tendencies of development, it has not been possible to determine the optimal points of gear change. For solving the resulting problems, better or worse solutions were proposed. However, even the best solutions require special commands for changing or completely eliminating general control programs under special conditions, such as ascent, overtaking, etc.
An objective of the present invention is finding the solution for the optimal control, by which ideal points of gear change can be determined for every condition of loading. That means ideal points of gear change, as could be determined by the driver in course of manual gear change.
The solution of the invention is based in part on the recognition that neither the position of the throttle pedal nor the extent of throttling express accurately the real state of loading, as the actual torque delivered by the motor also depends on the prevailing number of revolutions. As a matter of fact, the possibility or necessity of gear change depends on the extent to which the torque delivered by the motor is meeting the requirement of torque which is needed for travel of the vehicle in accordance with the intentions of the driver. Accordingly, the two torques enable a conclusion on the actual load, and said conclusion can be drawn most advantageously from the input/output numbers of revolutions of the hydrodynamic torque converter.
A further recognition is that, if changes in the load and causes are continuously analyzed, correction of the points of gear change is to be performed continuously but only to the extent necessary.
Accordingly, the invention relates to process for the gear change of the automatic transmission of a motor vehicle. From signals characterizing the r.p.m. of the motor and the output of the transmission a slip signal proportional with the slip of the torque converter is generated. Thereafter this slip signal is compared in an evaluating unit to a predetermined upshift slip signal and to a predetermined downshift slip signal. If the signal of r.p.m. exceeds the signal of the upshift r.p.m., and the slip signal is reduced below the predetermined upshift slip signal, a command signal for upshift is given to the electromagnetic valves of the transmission. Thereafter, if the chosen signal of r.p.m. falls below the predetermined downshift signal, or the slip signal exceeds the slip signal for downshifting, a command signal is given for shifting into a lower gear.
With a preferred mode of realization of the process according to the invention the signal characterizing r.p.m. of the motor, or the signal characterizing output r.p.m., is compared in a comparator with a signal characterizing the desired r.p.m. for direct engagement of the friction clutch or with a predetermined signal characterizing the value of the r.p.m. for releasing the clutch. The slip signal is also compared with a predetermined slip signal characterizing the slip value of clutch engagement. If the chosen signal of the number of revolutions exceeds the signal characterizing the clutch engagement r.p.m. and if the slip signals falls below the slip signal of clutch engagement, a command signal is given for closing the friction clutch. If the chosen signal of r.p.m. falls below the signal characterizing r.p.m. for releasing the clutch, a corresponding command signal is emitted.
With another preferred mode of realization of the process according to the invention the signal characterizing output r.p.m. or the signal characteristic for the r.p.m. of the motor is fed into a memory. Thereafter, by using the downshift command signal of the gear change control unit, the signal corresponding to the momentary r.p.m. at downshift is stored. Thereafter, by the aid of the unit forming the comparative slip signal, the upshift slip signal and/or the clutch engagng slip signal is reduced by a correction value depending on the stored signal of r.p.m.
With the third possible mode of realization of the process according to the invention the signal characterizing the output r.p.m. or the signal characterizing the r.p.m. of the motor is fed into a memory. By using the downshift command signal of the gear change control unit the signal characterizing momentary r.p.m. at downshift is stored. Thereafter, by the aid of the unit forming the comparative signal of r.p.m., the signal of upshift r.p.m. and/or clutch engaging r.p.m. signal is increased by the correction value depending on the stored signal characterizing momentary r.p.m. at downshift.
With the fourth advantageous mode of realization of the process according to the invention in the unit evaluating the number of revolutions, upon the downshift command signal of the gear change control unit, by increasing the signal of r.p.m. of upshift and/or the signal of r.p.m. of clutch engagement by predetermined value, comparison is performed with a signal with increased severity characterizing increased r.p.m. of upshift, and/or with the signal with increased severity characterizing increased clutch engagement r.p.m.
With the fifth preferable mode of realization of the process according to the invention, in the slip evaluating unit, upon the downshift command signal of the gear change control unit, the upshift slip signal and/or clutch engagement slip signal is reduced by a predetermined value. Subsequent comparisons are therefore performed with an upshift slip signal of increased severity and/or with a clutch engagement slip signal of increased severity.
In a sixth possible mode of realization of the process according to the invention, a signal characterizing the change in output r.p.m. is generated, or a signal characterizing the change in the number of revolutions of the motor is formed. Optionally, from the slip signal, a signal is generated which is characteristic of the change in load. Thereafter, upon receiving a downshift command signal, a constant "normal" upshift signal is formed if (i) either the signal characterizing the change of output r.p.m. or the signal indicating the change of r.p.m. of the motor is negative and (ii) the signal of the r.p.m. of the motor is below a limit value, or the signal indicating a change in load is negative. If there is (i) a positive signal characterizing the change in output r.p.m. or a positive signal characterizing the change in r.p.m. of the motor, and (ii) the signal of the r.p.m. of the motor is above the limit value for downshift or there is a positive signal indicating change in load, a constant "overtaking" upshift slip signal is generated. Finally, with (i) a signal indicating a negative change in out r.p.m. or with a negative signal characterizing change in r.p.m. of the motor, and (ii) a signal of r.p.m. of the motor lying above the limit value or a signal indicating a positive change in load, a constant "ascent" upshift slip signal is selected, and in the comparator the actual slip signal is compared with them.
With a seventh possible mode of realization of the process according to the invention, when a downshift command signal is derived from a negative signal characterizing change in output r.p.m. or from a negative signal indicating change in r.p.m. of the motor, and the signal of r.p.m. of the motor is above a limit value, or there is a positive signal referring to change in load, a constant "ascent" upshift signal is formed. In any other case, a constant "normal" upshift slip signal is generated, and the actual slip signal is compared to said signal in the slip evaluating unit.
Finally, with a preferable mode of realization of the process according to the invention, the upshift slip signal and the clutch engagement slip signal are identical. If the slip signal is below the upshift slip signal and the selected signal of r.p.m. is above the upshift r.p.m. signal, simultaneously with the upshift command signal an inhibiting signal is forwarded to the clutch engagement control unit.